Radio receiver



. April 29, 1947. I E, AB|N ET AL 2,419,569

RADIO RECEIVER r Filed May 24,l 1943 2 Sheets-Sheet l o v 14 9 I' f2 17. aman/l' l 16 BY @JW ATTH/VEY April 29 1947- E. LABIN ET AL. A 2,419,569

IRADIO RECEIVER Filed May 24, 1945 2 Sheets-Shet 2 mwa/Wm M A My/w Patented Apr. 29, 1947 RADIO RECEIVER Emile Labin, New York, and Donald D. Grieg,

Forest Hills, N. Y., assignors to Federal Telef phone and Radio Corporation, Newark, N. J., a

corporation of Delaware Application May 24, 1943, Serial No. 488,181

(Cl. Z50-20) 14 Claims. 1

This invention relates to radio receiving circuits and more particularly to radio circuits for translation of radio frequency pulses.

It is known that intelligence may be transmitted through wire or space by modulating a carrier wave in the form of a train of pulses wherein the intelligence is represented by variation in time such, for example, as Variations in the time interval between pairs of pulses called double pulse modulation. The duration of th'e pulses of the double pulse modulated wave are usually constant and small compared with the time intervals between adjacent pulses. In this kind of pulse modulation whether for transmission of voice, pictures, telegraph code, facsimiles or other intelligence, the pulses are preferably of equal amplitude and the modulation is deter-v mined solely by time displacement.

It is one of the objects of our invention to provide a circuit for translating such time modulated pulse carrier waves into equivalent trains of time modulated impulses of greatly amplified intensity.

Another object of our invention'is to provide a radio receiver for time modulated pulse reception which is relatively simple and which requires only a small number of parts.

Still another object of ourinvention is to provide a single translation stage for translating time modulated pulse carrier waves into a train of time modulated impulses having an unusually large gain and a high signal-to noise ratio.

The principles of our invention are accomplished, for example, by a triggerable oscillating circuit having an output of impulses corresponding in occurrence to the pulse occurrence of a time modulated carrier wave or other time modulated pulse source applied thereto. The oscillating circuit is adjusted for normal interval operation at a frequency lower than the unmodulated frequency of a given carrier wave or other pulse source. The pulses of the source control the oscillation intervals of the circuit, and by providing a local pulse generator such as a multivibrator which is in turn controlled by the oscillation intervals of the oscillating circuit, rectangular impulses of constant predetermined duration having occurrence variations corresponding to th'e pulse occurrence of the carrier wave are produced. The rectangular impulses of the multivibrator may in turn be applied to the control circuit of the oscillating circuit to increase the sensitivity and stability thereof during the operating intervals thereof.

-'Iheoutput impulses thus produced may be apdetected in the usual manner.

plied to any desired form of T. M. (time modulation) demodulator such, for example, as disclosed in U. S. Patent to Reeves 2,266,401, or the copending application of D. D. Greig Serial No. 459,959, led September 28, 1942. The demodulation of the pulses translates the intelligence represented by the time variations thereof into corresponding amplitude variations which' may b For a further understanding of the above and a further embodiment of the invention, referencel may be had to the following detailed description to be read in connection with the accompanying drawings, in which:

Fig. 1 is a block diagram of one form of T. M. (time modulation) receiver in accordance with our invention;

Fig. 2 is a schematic wiring diagram of the oscillating trigger circuit of the embodiment shown in Fig. 1;

Fig. 3 is a graphical illustration showing the translation operations of the circuit of Fig. 2;

Fig. 4 is a schematic wiring diagram of another embodiment of our invention showing a simplied translating circuit; and

Fig, 5 is a graphical illustration showing the operating steps of the circuit in Fig. 4.

Referring to Fig. 1, the T. M. receiver therein shown for purposes of illustration includes the usual antenna I Il, an oscillating trigger circuit I'2, a multivibrator circuit I4 and a T. M. (time modulation) demodulator I6. The oscillating circuit I2 controls operation of the multivibrator I4 and the multivibrator furnishes a feed-back voltage to the oscillating circuit. The normal operation of the oscillating circuit produces intervals or groups of oscillations and the occurrence of each group operates to trigger the multivibrator I 4 from a rst state of operation to a second state of operation from which it is adapted to return to the rst state after a predetermined interval. This operation of the multivibrator produces a voltage impulse of rectangular form which is fed back to the oscillating circuit to increase the sensitivity and stability thereof during its operating intervals. The multivibrator pulses, correspond in occurrence with the pulse occurrence of the modulated carrier wave and their duration may be controlled independently of the operating interval of the oscillating circuit. Either the multivibrator pulses'or the average voltage pulse of the operating interval of the oscillating circuit may be applied to the demodulator I 6 by selective operation of the switch I'I with respectto connecljtions i9 and 31.

As shown in Fig. 2, an L-C resonant circuit is tuned to a particular carrier wave the R. F. energy of which is obtained from the antenna coupling coil lo. The oscillating circuitlZ is provided with a vacuum tube having an anode 2l, a control grid 22, a cathode 23 and a screen grid 24. Gne side of the L-C circuit is oonnected through a blocking condenser 25 to the grid 22. The opposite side 2l of the L-C circuit is grounded. To complete the triggering circuit, the cathode 23 is connected to the coil L at 28. The screen grid 24 is connected to ground through a condenser 3E! for by-passingthe radio frequency energy. The screen grid isV alsoconnected to a movable contact of a potentiometer 32l which is supplied with' positive energy from a battery terminal 34. The plate output circuit 35jis`fconnected across a load resistance S to the battery terminal 34.

'I he multivibrator I4r is of known character having onestate of operation from which it is capable ot beingY triggered to-a secondstatey of operationfrom'which it will return after a given intervalof time to the rst stateof operation. The 'output ofthe multivibrator is preferably used asthe time modulation output impulses since the duration thereof can-be controlled independently O'th'eoperating interval of the oscillating circuit o f tube 2G.

By feeding back energy off the multivibrator pulse'output over-connection 37 to a voltage divider R1 and-R2 tothe grid22, the sensitivity of thetube is greatly increased during the operating interval thereof. In other words, the multivibrator pulsesinsurecontinued oscillations of the circuit! forv the duration of theV multivibratorv pulses, thereby stabilizing the duration of the successiveinterval operations ofthe circuit. The resistorY R1 is preferably high to-providea'high impedance to the R. F. energy of the grid circuit. I'fndvesiredthe feed-back connectionV maybe made to the screen grid 24 in place of grid- 22;

InFig., 3', curve ciA represents a period A ofvnor mal operation in absence of input signals and a,`

period BN during which input signals are received. Curve b representsgenerally the gridvoltage of gridNZZ during the periods representedV by curve a.' Curves c, eiland e represent respectively, the

voltage impulses produced by the multivibrator,

the oscillation intervals of the oscillating circuit and lenvelope pulses produced from the. oscillating energy.

that noinput pulses are received` (period A), the operation ofthe oscillating circuitl` mand the multivibrator I4 may loe described v as-follorws.` When the potential on the grid 22 builds up to a critical value. indicated by thelevel 40,- curve b, oscillationsrwill be initiated by thermail orrandom-noise voltage fluctuations such as indicated lat 4i.. The oscillations build-up rapidly as indicated by curved and trigger themultivi'- brator` {4g-from one statelof operation-to a second state of operation thereby producing at the outputthereof a pulse 42' (curve c) of rectangularv 45- of! curvee. The-oscillating yinterval and' there- I fore the envelopes 45 are termnatedby the buildi ing-up of a negative charge on the condenser 26 to a value represented by the negative level 46.

A period free from oscillation follows the occurrence of each envelope during which the grid voltage becomes gradually less negative by leakage through resistors Ri, R2 until the grid voltage again reaches the critical level lill. In the absence of incoming pulses the initiation of oscillation is dependent upon random noise voltage fluctuations as indicated at 4i and therefore the normal period To of the oscillation intervals may vary. When this frequency of operation is lower than the unmodulated pulse repetition frequency ofl the-carrier wave (see period Ts), the signal pulses of' the carriery wave will operate to initiate the oscillation intervals prior to the grid voltage reaching thecritical level 4B.

The pulse modulation of the carrier wave is represented in curve a by the signal pulses 5I, 52 and 53, 5d wherein the signal pulses :are in pairs as indicated andthe maximum degree of modulation is represented by the difierence in the intervals t1 and t2. This double pulse modulation is chosen for purposes ofA illustration, it being understood that other forms of pulse modulation may received where the translation is'made into voltage impulses oi a selected width according.` to Iadjustment of the multivibrator. shown, the pulse Elfoccurs prior to thegrid voltage reaching the levellliif andthe energyof the pulse. when superimposedA on the grid voltage, (curve b) increases the grid voltage sharplyvabove the level 453i thereby initiating the oscillation-interval incoincidence with the leading edgeof'the.

pulse 5l. The leadingedges of the oscillations tid, envelope 54e and the impulse 5100i themultivibrator, are all insubstantialrcoincidence.

with the leadingfedge offthe pulse 5|.

Likewise, pulses 52V; 53 and 5.4 synchronize the operation ofthe oscillatingtrigger circuit tov pro-.-v

leading edges of, the impulses of curves c and e.

correspond in time displacement to, the; time ,displacement of the pulses of the'modulated; carrier wave of curve d and maybe demodulated in the demodulatorv iii in the manner disclosed in the aforesaid application Serial No. 459,959. The impulses of curve c are preferred for demodulation since their amplitudes-are constant and the WidthA of suchfpulses may be controlled independently of the oscillatingintervals.

Referringgtoligs; i and 5, they oscillating circuitfmultivibrator arrangementg'of Figs. 1 and-2 is replaced by a simplined oscillating circuit from which direct current impulses are obtained in; response to theoscillation intervals; of the oscil-i lating circuit.` The circuit of Fig. 4f comprises the usual antenna iii which is `applied to anin'- ductance; coil 621 through a ccuplingcondenser Si and-*an adjustable contact 63.; is connected inparallel with an adjustable condenser Sill tunable toftl'i'e R. frequencyv of pulse modulation carrierwaves., A" further tuning ofl the carrier wave detecting circuitv 62,` 64.7is .proe vided by a second'ad-justablecondenser lwhch is connected betweeny oneA side` of the resonant circuit andv ground. The side 67 ofv the resonant circuity is connected` to tliey anode iiipiofk arvacuum tubes l The. side 'of the resonant circuit is connected through ablocking condenser 72 tov The cathode 74 is connected-LA a control grid i3. tog'round; An adjustable grid/leak! resistorl 15 Asv It is readily apparent from an inspection,

The coil 62 i,

for the grid 'i3 is also connected to ground. The plate circuit of the tube is supplied with apositivel potential from a battery terminal'l through a resistor 'l1 and an R. F. isolating inductance coil 'I8 to the side 69 of the resonant circuit. Connected to this circuit between the resistor 'I1 and the coil 'I8 is an output connection 19 which is applied to the T. M. demodulator Sii.

yThe loperation of this circuit is similar to the circuit of Fig. 2 except that the oscillations applied across the plate and grid of the tube provides a flow of rectified current through the plategrid circuit thereby building-up a negative voltage charge on the blocking condenser 12. The operating steps are illustrated by curves g, h, i and :i of Fig. 5. Similarly as in the circuit of Fig. 2, each series of oscillations (curve i) produces a negative voltage (curve h) which build up on the condenser 12 until level 82 is reached thereby blocking the oscillations. The coil 'I8 blocks passage of the radio frequency component while permitting passage of the direct current component producing the voltage pulse across resistance 17. These pulses 85 are represented by curve y. The intelligence represented by their displacement by pairs (the extreme'degree of displacement being represented by theintervals t3 and t4 between the successive pairs of pulses) may be demodulated in the usual manner by the demodulator 80.

From the foregoing description it is readily apparent that in accordance with our invention the negative value of the grid potential during the intervals between input signals is such as to maintain the circuit non-responsive to most noise voltage fluctuations thereby providing a high signal-to-noise ratio for the receiver. Further, the feed-back feature of the embodiments herein disclosed greatly increases desirably the gain of the triggering circuit.

While we have shown the principles of our invention in connection with specific apparatus, it is to be understood that the illustrations are given by way of example only and not as limiting the scope of the invention as set forth in the objects and the appended claims.

We claim:

1. A radio receiver for time modulated pulse reception, comprising an oscillating trigger circuit having normal interval operation at a lower frequency than the unmodulated pulse repetition frequency of a given time modulated pulse source, means controlled by the oscillations occurring in the oscillating circuit for each operating interval to produce a voltage impulse, means to apply energy received from said pulse source to said circuit to synchronously control the operation thereof, whereby the impulses produced correspond in occurrence to the pulse occurrence of said source, and means for demodulating the impulses.

2. The radio receiver dened in claim 1 wherein the means for producing said impulses includes a multivibrator having a mode of operation initiatable by the occurrence of oscillations in said oscillating circuit.

3. The radio receiver defined in claim 1 wherein the means for producing said impulses includes a condenser-resistor combination adapted to build-up a blocking voltage in response to oscillations in said circuit and to control the dissipation of the blocking voltage at a given rate selected in accordance with the unmodulated pulse repetition frequency of said pulse source.

4. The radio receiver defined in claim 1 wherein the means for producing said impulses includes a multivibrator, means to apply the output of said oscillating trigger circuit to said multivibrator whereby the occurrence of oscillations causes the multivibrator to chan-ge from one state of operation to a second state of operation from which the multivibrator returns after a predetermined operation, and means to apply the impulse output of said multivibrator to the oscillating trigger circuit to increase the sensitivity thereof during the oscillating interval thereof.

5. The radio receiver dened in claim 1 wherein the oscillating trigger circuit includes a vacuum tube having plate, grid and cathode electrodes, said grid and cathode electrodes being connected to the means for applying energy of said pulse source, means connected to the plate electrode for supplying the output impulses in response tov oscillations established in the tube circuit, and means adjustable to control the bias of said tube.

eration at a lower frequency than the unmodulated pulse repetition frequency of said pulse source, a multivibrator controlled by the occurrence of oscillations in said circuit for producing for each interval of operation an impulse of given duration, and means to apply energy of said given source to said circuit to synchronously trigger the operation thereof whereby the impulses produced by said multivibrator correspond in occurrence to the pulse occurrence of said source.

7. The circuit defined in claim 6, in combination with means to apply impulse energy from the multivibrator to the oscillating trigger circuit to increase the sensitivity thereof during oscillating intervals.

8. A circuit for translating the pulses of a time modulated pulse source into an equivalent train of time modulated impulses comprising an oscillating trigger circuit, means adjustable to establish the normal interval operation of said oscilating trigger circuit at a lower frequency than the pulse repetition frequency of said given source, said circuit having a vacuum tube with plate, grid and cathode electrodes, an inductance-capacitance circuit tunable to receive energy of said given source, said inductance-capacitance circuit being connected across certain of the electrodes of said tube to provide a tube circuit in which initiation of oscillations is caused by the pulse energy of said source, and means controlled by the oscillations occurring in the tube circuit for producing an impulse, whereby the occurrence of pulses in said source operate to generate through the medium of said oscillating trigger circuit a train of impulses which correspond in occurrence to the pulse occurrence of said source.

9. The circuit dened in claim 8 wherein the means for producing the impulses includes a multivibrator having a, mode of operation initiatable by the occurrence of oscillations in said tube circuit, the plate electrode of said tube circuit being connected to the input of said multivibrator, and feed-back means connecting the output of said multivibrator to one of the electrodes of said tube. v

10. The circuit dened in claim 8 wherein the tube includes a, screen grid electrode and means to apply a source of voltage to said screen grid to control the normal operating frequency of the oscillating trigger circuit, and the means for producing the impulses includes a multivibrator havmem-aaai ingfia, moda of operation initiatableby the: occur+ rencei of; oscillations in said: tubetcircuitand 'iced-- build-up a negative: charge during: oscillations in;

said tube; circuit', therebyv providing; aV blocking voltagev fon theitube, and1said: resistor operating asa grid'leakito `control thedischarge ofthe nega.-`

tive charge upony saidi condenser.

12:` A'circuitt for translatinga pulse.- modulated carrier into impulseenvelope form comprsingan oscillating; trigger circuitV havingfnormal interval operationata lower pulsing frequency thanithe unmodulated pulse repetitionfrequency of said.

carrienmeans controlled;` by the oscillationsocf curring inthe oscillatingi circuit to produce. a voltage impulse of envelopeiorrnzfior'each oscillating operating interval, and means to apply pulse modulatedcarrier energyA to said circuit to synchronously controll the operation thereof, Wherebythe impulses producedcorrespond in occurrence; toi-thefpulse modulation of said carrier.

mea-ns. for. producing said: impulses. includes: a

multivibrator-havinga mode of operation initiable f by.' the occurrenceA` ofY oscillations' in said oscillating: circuit.

14;, The circuitfdened in claim 12 wherein'the means forY producing said impulses includes a condenser-resistor combination adapted no-buildupa blockingvoltagein response to oscillationsin said'v circuit and to control the dissipation of" the blocking Voltage at a given rate selected in aocordancewith the pulse repetition-frequency of said` carrier wave.

EMILE LABIN. DONALD D. GRIEG;

REFERENCES CITED Tliezffo'llowii'ig references are of. record in` the'.

file off'this-patent:

UNITED STATES PATENTS,

Number Name Date 2,323,596 Hansell July, 1943 1,919,985 Pattersonv Julyj25, 1933 2,266,401' Reeves Dec. 16, 1941 

